DIY: Building a Dobsonian Telescope At Home

(Last Updated On: April 15, 2018)

Dobsonian Telescopes are the simplest types of telescopes. They are easy to use, are strong and robust and inexpensive. They are popular with astronomers of all levels of experience and training, from beginners and amateur hobbyists to professionals and experienced scientists.

Dobsonian telescopes get their name from their creator, John Dobson, who combined the simplicity of a Newtonian telescope with an Alt-Azimuth mount.  Here’s how a typical Dobsonian telescope looks like:

[Source: https://www.universetoday.com/84285/why-are-dobsonian-telescopes-a-favorite-among-amateur-astronomers/]

Dobson made the telescope completely from simple, ordinary household items; a process that you can replicate yourself. Just follow this DIY guide to building a Dobsonian telescope at home.

Skywatcher 10 inch Dobsonian.

[Credit: sherwoods-photo.com]

1) Building a Dobsonian Telescope At Home

Why Build a Dobsonian Telescope Yourself?

Dobsonian telescopes have a very simple reflector design, which is why they are very easy to make at home. Sure, you will save money by building a Dobsonian telescope, but it’s not really about saving money as Dobsonian telescopes are never too expensive in the first place.

It is more about giving you a sense of accomplishment from building a technically advanced product that can be used in various scientific experiments.

This is a great feeling; you will feel like you have achieved something, this is much more satisfying than simply buying a telescope from the market.  You will enjoy watching the night sky with the Dobsonian telescope you have made yourself much better in this manner.

You can start by downloading the PDF version of the book, Plans for Building a Sidewalk Telescope by John Dobson and learn from the master himself.

Also, watch this YouTube video where Mr. Dobson shows you how to build a Dobsonian telescope. This video was made shortly before his death in 2014. (What a great man!)

Follow the Step-by-Step Guideline Given Here to Build Your Own Dobsonian Telescope

 Step #1: Choose the design and aperture size.

The first step to building a Dobsonian telescope is to choose the aperture size and the focal length. The aperture size is the diameter of the primary mirror.

Once you choose the right aperture size and focal length, enter them into a design program such as Newt-Web, which takes these inputs to create a Dobsonian telescope as per your specifications.

Step #2: Buy the parts and tools you need for this task.

Once you have decided on the design, buy the parts and tools you need directly off the market, or for free from many construction materials that’s lying around at your house or in the neighborhood. You will get everything you need from the local hardware store.

Here’s a list of items you need to build the Dobsonian telescope.

  • Woodworking tools
  • Electric drill
  • Telescope tube
  • Primary mirror
  • Secondary mirror
  • Spider
  • Teflon
  • Ebony star strips
  • Mirror cell
  • Focuser
  • Stain
  • Nuts and Bolts
  • Washer
  • Baltic birch sheets
  • Telrad base
  • Medical cotton
  • Silicone adhesive
  • Birch veneer

 Step #3: Build a simple optical tube.

To build the Dobsonian telescope, you need to construct a simple optical tube with baffles. Baffles are octagonal wood pieces that are placed within the tube which lend it support and help direct the light through the various mirrors and lenses of the tube.

You will need the right number of baffles. You can cut them out of wood and attach and secure to the long piece of plywood. Now secure the baffles in place and cover them with another layer of plywood – so as to give it the appearance of an optical tube.

An easier thing to do would be to buy a telescope tube directly from the hardware store; this will save you the trouble of constructing the tube yourself.

 Step #4: Mount the focuser on to the optical tube.

The focuser does the job of focusing the light as it comes through the telescope. The focuser is mounted on top of the tube – This is how it is done.

  • Choose the diameter of the focuser base – you will know this from the design program.
  • Drill a hole in the focuser base at the center and place the focuser in the hole.
  • Mark the spots where you want the bolts to go. Now take the focuser out and drill holes in that spot for the bolts to go in.
  • You can now replace the focuser and bolt it directly into the tube

 Step #5: Place the primary mirror in the mirror cell.

The next step is to mount the primary mirror and place it in the mirror cell. Do this very delicately; there should not be any bending of the mirror.  You can then tighten the clips of the mirror cell just a bit to hold the mirror firmly in place.

 Step #6: Place the mirror cell on to the optical tube.

Mounting the mirror cell onto the optical tube is easy. Place the mirror cell firmly in place with silicone adhesive pads and use bolts to fix the mirror in place. Secure the mirror cell to the telescope.

Step #7: Place the secondary mirror into the spider.

Next, you will need a spider and a secondary mirror, also called as a diagonal mirror. You can buy them at a hardware store. Mount the secondary mirror to the spider with an adhesive mount. Apply silicone adhesive t the holder before attaching the secondary mirror to it. Use toothpicks to ensure there is enough space between the mirror and the holder. Do the whole thing very carefully to prevent optical distortions, and allow it to dry for a day. The mirror will now be securely attached to the spider.

Step #8: Mount the spider with the secondary mirror to the optical tube.

The next step is to mount the spider to the optical tube. For this, use the measurements from the design program to determine where exactly to mount the spider and at what distance from the optical tube. Drill a hole in that spot and mount the spider in place.

 Step #9: Build the mount.

The optical tube is done. The last step is to build the mount. This requires some carpentry work. First, you will have to build the telescope base on which the tube rests on. Then, you need to build a holder for the optical tube which is of the right size to fit the telescope tube. Finally you will need to make a ground board, a round plywood piece that ensures that the mount is as stable as possible.

Step #10: You’re almost done!

Next, use Teflon pads to attach the base to the ground floor. Place the telescope within the holder and bolt the hold to the top of the base. That’s it, you have just built your first Dobsonian telescope. You may now raise a glass to the great John Dobson.

[Source: http://www.trbimg.com]

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